It seems like in the current build sometimes dox totally stop what they do and become entirely irresponsive untill you do like 9001 RMB commands. I also saw that the movement command was placed down. Sometimes selecting parts of the stuck guys and giving new commands seems to solve some of the problems. But by that time its usually toolate for you for that fight....
Yeah the latest PTE is pretty bad for dox movement. The last game I played, the only way I could get the dox to move was by giving them small area patrol commands for where I wanted them to move to! RMB was not doing ****.
IF your selection contains a stuck bot that can sometimes occur. If you select only the ones that aren't stuck then they should move just fine.
I just had a game with this issue, I completely lost the ability to move units, not only dox, but pretty much any units. After most of my base got trashed while my dox sat there uselessly, pathing slowly started to work again, just in time for a commander to get blown up.
This is my theory of why this happens. Units in move command will move at the speed of the slowest unit right. So, if you get one stuck unit due to bad pathing, it will report a move speed of nil. Then with a whole group selection of units that include that one unit, they will become 'unresponsive' to move order. This doesn't explain why even a-move doesn't work sometimes though.
I believe Elodea is right. Sometimes on for example metal planets they push eachother over a ledge, those guys become immobile and then the problem starts to occur.